1. Field of the Invention
This invention relates to an optical system in an apparatus or a measuring device using a semiconductor laser as a light source.
2. Description of the Prior Art
Generally, the light emitted from a semiconductor laser has different divergence angles in orthogonal directions. Diverging origins also differ in the orthogonal directions. This is attributable to the internal structure of the semiconductor laser itself, and more particularly to the fact that the area of the light emitting portion is in a rectangular form instead of a circular form as in a gas laser.
FIG. 1 of the accompanying drawings shows the diverging state of the beam from a semiconductor laser. FIG. 1(A) is a view of the semiconductor laser as seen from thereabove, and FIG. 1(B) is a view of the semiconductor laser as seen from the side thereof. In FIG. 1, reference numeral 1 designates the chip of the semiconductor laser, and reference numeral 2 designates the juncture surface. The diverging origin in a direction parallel to the juncture surface of the beam 3 (hereinafter referred to as the lateral direction) is indicated by 4, and the diverging origin in a direction perpendicular to the junction surface (hereinafter referred to as the longitudinal direction) is indicated by 5. The diverging origin 4 in the lateral direction is situated at a position spaced apart from the emergence surface, and the diverging origin in the longitudinal direction is situated at a position near the emergence surface.
As a method for correcting the difference in position between the beam waists in the longitudinal and lateral directions, there is a method as disclosed, for example, in Japanese Laid-open Patent Application No. 24542/1977 wherein the diverging origins in orthogonal directions are made coincident by cylindrical lenses of different curvature radii whose bus bars are orthogonal to each other.
The method of correcting such diverging origins by an optical system (this will hereinafter be referred to as the correction of A.sub.s) enables regularization of the beam waist positions and obtainment of a small image forming spot. This is not directed to obtainment of an image forming spot but is a condition required when the beam is simply collimated for use in an interference experiment.
However, correcting A.sub.s is a very serious matter to the adjustment of an optical system. That is, to cause different diverging origins in two orthogonal directions to be coincident at a single point, the same adjustment must be effected twice with respect to the two orthogonal directions and this is very cumbersome procedure. Moreover, the adjustments cannot always be effected independently of each other, but when one is adjusted, the other may get out of order and thus, the adjustments require skilled technicians.
Further, the quantity of such A.sub.s is not constant but differs from one semiconductor laser to another. Not only in lasers of different construction but also in lasers of the same construction, the quantity of A.sub.s fluctuates depending on the manufacturing lot. Accordingly, correcting such A.sub.s in an optical system premises the change of the optical system for individual semiconductor lasers or the provision of an adjusting mechanism, and this leads to an increased burden of the optical system and increased cost and cumbersomeness. Furthermore, even in the same lasers, the quantity of A.sub.s may also be varied by current value.
On the other hand, where a semi-conductor laser is used for image recording or display, unlike the case where it is used for interference experiment, there is no necessity of regularizing the diverging origins. This is a problem concerned only with the shape of the image forming spot and the peak power, and correction of A.sub.s will be unnecessary if the specification necessary for effecting image recording or display is satisfied.